Elevated CO2 impairs plants defense mechanism against insects

March 25th, 2008 - 2:30 pm ICT by admin  

Washington, March 25 (ANI): A new study has indicated that elevated carbon dioxide impairs a key component of the defenses of plants against leaf-eating insects.

The study, carried out at the University of Illinois, took into consideration the soybean plant, whose defenses go down as CO2 goes up.

The new study, led by entomology professor and department head May Berenbaum, used the Soybean Free Air Concentration Enrichment (Soy FACE) facility at Illinois.

This open-air research lab can expose the plants in a soybean field to a variety of atmospheric CO2 and ozone levels without isolating the plants from other environmental influences, such as rainfall, sunlight and insects.

High atmospheric carbon dioxide is known to accelerate the rate of photosynthesis. It also increases the proportion of carbohydrates relative to nitrogen in plant leaves.

The researchers wanted to know how this altered carbon-to-nitrogen ratio affected the insects that fed on the plants. They predicted that the insects would eat more leaves to meet their nitrogen needs.

When they exposed the soybean field to elevated carbon dioxide levels, the researchers saw the expected effect: Soybeans in the test plot exhibited more signs of insect damage than those in nearby plots.

A closer inspection showed that soybeans grown at elevated CO2 levels attracted many more adult Japanese beetles, Western corn rootworms and, during outbreaks of Asian soybean aphids, more of these than soybeans in other plots.

The team then turned its attention to the hormonal signaling pathways of the plants, focusing on a key defensive chemical the plants produced to ward off an insect attack.

When insects eat their leaves, soybeans and other plants produce a hormone, jasmonic acid, that starts a chain of chemical reactions in the leaves that boost their defenses. Normally, this cascade leads to the production of high levels of a compound called a protease inhibitor. When the insects ingest this enzyme, it inhibits their ability to digest the leaves.

What we discovered is that leaves grown under high CO2 lose their ability to produce jasmonic acid, and that whole defense pathway is shut down, said Evan DeLucia, an author of the study. The leaves are no longer adequately defended, he added.

The higher carbohydrate content of the leaves and the lack of chemical defenses allowed the adult insects to feast and live longer and produce more offspring.

The researchers, both of whom also are affiliated with the universitys Institute for Genomic Biology, will now seek to determine whether the same process occurs in other plants. (ANI)

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